1. Technical Field of the Invention
This invention pertains to the management of system resources in a Telnet environment, and more particularly to the use of a round trip time (RTT) value for recovering server system resources used by a Telnet client which has become inactive.
2. Background Art
TCP/IP Telnet servers use a timing mark (Telnet Timing Mark Option, RFC 860, May 1983) to determine if Telnet clients have received and processed any transmitted data, or even if they are still connected to the server. The Telnet server periodically (i.e., every 10 minutes) sends a query called a timing mark to the client, and interprets any failure to reply to the timing mark as an indication the client is no longer active or connected to the server. This is a highly desirable function in Telnet servers, as it allows servers to reclaim system resources from clients that are no longer active or connected. The RFC 860 timing mark is used as an indicator that the client has processed a data stream up to this point. As part of this process, the client must send a reply to let the server know that it did indeed get the timing mark query and thus the server knows that all data up to the timing mark got processed.
Since Telnet servers are not typically configured with a transport layer round trip time (RTT) value to determine the maximum time to wait for a reply to a timing mark query, they tend to wait a very long time for replies. The actual wait tends to be a function of the transport protocol (TCP) layer, which is not visible or configurable by the Telnet server. This is unsatisfactory, as most transport protocols use RTT values that are very large time periods in TCP/IP, often values larger than system administrators would like to configure.
TCP/IP can run across a Wide Area Network (WAN), and the response time across a WAN can be considerably larger than across a Local Area Network (LAN). The combination of WAN and LAN clients on any Telnet server can have RTT periods which vary by many seconds or even minutes. This makes it difficult to pick a suitable RTT value that will work for all clients unless a very large value is selected. The larger a value selected, the longer to recover unused system resources.
It is an object of the invention to detect a lost session.
It is a further object of the invention to provide at the application level recovery of system resources used by a Telnet client as quickly as possible after the client has become inactive.
It is a further object of the invention to provide an application level inactivity timer for a Telnet client that will work across any kind of network, allowing quick reclamation of any system resources which may be locked up by a no longer connected or active client.